1. Field of the Invention
This invention relates to a process for producing an electrophotographic photosensitive member.
2. Related Background Art
Electrophotographic photosensitive members making use of organic photoconductive materials have, e.g., a charge generation layer containing a charge-generating material and a surface protective layer containing a conductive material and a lubricant. These layers are formed by coating a dispersion prepared by dispersing the corresponding materials in a resin, followed by drying.
Dispersion means conventionally used to prepare such a dispersion include roll mills, ball mills, attritors, sand mills and high-pressure dispersion mixers. The roll mill dispersion is a method in which a fluid (liquid) mixture comprised of a pigment, a binder resin and a solvent is passed between two or more rotating rolls to carry out dispersion, but are not so widely used in recent years because of a disadvantage that they have a very poor productivity.
The dispersion carried out using ball mills, attritors or sand mills is a method in which a pigment, a binder resin, a solvent and so forth are put in a vessel (dispersion vessel) together with a medium (dispersion medium) and are stirred by some means to effect dispersion by the aid of energy produced by collision or friction between medium beads.
However, in the case of dispersions (fluid dispersions) for electrophotographic photosensitive members, dispersion must be effected especially microscopically and in a narrow particle size distribution. In these dispersion methods, it is difficult to obtain dispersions formed microscopically and in a narrow particle size distribution. These methods are also unsatisfactory in view of productivity. Also, fragments of the vessel and medium may become included in dispersions to damage the properties of electrophotographic photosensitive members. Electrophotographic photosensitive members obtained by production processes making use of such dispersions tends to cause spots (black spots or white spots) and image fog.
As a different dispersion method, as disclosed in Japanese Patent Application Laid-open Nos. 4-337962 and 4-372955, a high-pressure dispersion method is available in which a fluid mixture containing a pigment and a dispersion solvent is led into a dispersion chamber having an orifice, under application of a high pressure to cause the fluid to collide against one another at a high velocity in its channel leading to the orifice, to carry out dispersion.
In such a conventional high-pressure dispersion method, however, it is impossible to obtain dispersions formed well microscopically and in a narrow particle size distribution, and electrophotographic photosensitive members produced using such dispersions may cause spots and image fog in some cases.
In such conventional high-pressure dispersion, the dispersion chamber has a structure wherein a channel is provided therein with a branching zone and a joining zone to cause the fluid mixture to collide against one another (FIG. 6), or a structure wherein a channel is bent to provide a bent zone to cause the fluid mixture to collide against walls. (FIG. 7). Thus, since the fluid mixture undergoes dispersion in a microscopic time passing through a microscopic volume, the dispersion can not be effected well uniformly to tend to cause over-dispersion at some portions of the fluid mixture and insufficient dispersion at its other portions, and it is difficult to effect uniform dispersion. Accordingly, in some cases, the step of dispersion must be repeated plural times to ensure necessary properties, and it has been sought to more improve productivity.
In particular, a charge-generating material oxytitanium phthalocyanine tends to cause crystal transformation during the dispersion. Also, azo pigments and fluorine resin powders may agglomerate to make it impossible to achieve any good uniformity in some cases.
In addition, in the conventional high-pressure dispersion, the dispersion chamber may greatly wear at the branching zone, joining zone and bent zone of its channel to make dispersions have an unstable quality because of the wear of its channels. Moreover, such a dispersion chamber requires a high production cost and the dispersion machine requires a high maintenance cost. Furthermore, because of the branching zone, joining zone and bent zone present inside the dispersion chamber, it has been difficult to perform maintenance or disassembly cleaning.
An object of the present invention is to provide a process for producing an electrophotographic photosensitive member by which materials to be dispersed can be dispersed microscopically and in a narrow particle size distribution and can be dispersed in a good productivity and stably at a low cost.
Another object of the present invention is to provide a process for producing an electrophotographic photosensitive member which may hardly cause faulty images such as spots and image fog.
The present invention provides a process for producing an electrophotographic photosensitive member having a layer; the process comprising the step of forming the layer by the use of a dispersion obtained by ejecting a pressurized fluid from an orifice into a hollow member having a diameter larger than the diameter of the orifice, to disperse a material to be dispersed; the fluid being ejected in substantially an unatomized state.